In the art of container manufacture, the term "container finish" generally refers to that portion of the container that defines the container mouth. In a bottle, for example, the finish includes that portion of the container neck having threads and/or shoulders for receiving the container cap, as well as the upper surface of the neck surrounding the container mouth against which the cap seats. It is important that the container finish be properly manufactured so that a cap may be affixed thereto to seal the container cavity against leakage and escape of carbonation during handling and storage.
Conventional technology for mass production of glass or plastic containers involves forming the containers in a multiplicity of molds. Various types of faults or checks, termed "variations" in the art, may occur. It has heretofore been proposed to employ optical scanning techniques for inspecting such containers for variations that affect optical transmission characteristics of the container. In U.S. Pat. Nos. 4,378,493, 4,378,494 and 4,378,495, all of which are assigned to the assignee of the present application, there are disclosed methods and apparatus in which glass containers are conveyed through a plurality of stations where they are physically and optically inspected. At one inspection station, a glass container is held in vertical orientation and rotated about its vertical axis. An illumination source directs diffused light energy through the container sidewall. A camera, which includes a plurality of light sensitive elements or pixels oriented in a linear array parallel to the vertical axis of container rotation, is positioned to view light transmitted through a vertical strip of the container sidewall. The output of each pixel is sampled at increments of container rotation, and event signals are generated when adjacent pixel signals differ by more than a preselected threshold level. An appropriate reject signal is produced and the rejected container is sorted from the conveyor line.
U.S. Pat. No. 3,880,750, likewise assigned to the assignee hereof, discloses an electro-optical gauge specifically adapted for inspecting the sealing surface of a container finish. A light source is positioned above the container and directs a light beam at constant intensity downwardly onto the sealing surface as the container is rotated. A camera has a single sensor positioned to receive light energy reflected by the sealing surface and provides an analog output to associated scanning electronics. The sensor output is monitored as the container is rotated about its axis, and commercial variations at the sealing surface, such as line-over-finish or LOF . variations, open or closed blisters and unfilled finish variations, are detected as a function of variations in sensor output amplitude.
U.S. Pat. No. 4,701,612, assigned to the assignee hereof, discloses a method and apparatus for inspecting the finish of transparent containers, particularly glass containers, that include facility for directing diffused light energy laterally through the container finish as the container is rotated about its central axis. A camera includes a plurality of light sensitive elements or pixels disposed in a linear array angulated with respect to the container axis and coplanar therewith to view the external and internal finish wall surfaces, the latter through the open canister mouth. Individual elements of the camera linear array are sampled by an information processor at increments of container rotation, and corresponding data indicative of light intensity at each element is stored in an array memory as a combined function of element number and scan increment. Such data is compared, following completion of container rotation, to standard data indicative of an acceptable container finish, and a reject signal is generated if such comparison exceeds an operator-adjustable threshold.
U.S. Pat. No. 4,454,542 discloses apparatus for inspecting the sealing surface of containers in which an annular light source is positioned above and coaxial with the container mouth to direct light energy through a diffuser onto the sealing surface. A camera is positioned above and coaxial with the light source and container to view the sealing surface through the central opening of the light source. The camera includes a CCD area array of light sensitive elements that receives the entire image of the container sealing surface as the container is held stationary. The area image is scanned to identify commercial variations as a function of light reflected from the sealing surface.